Preparation of monocyclic aromatic hydrocarbons from industrial lignin residue and polyethylene co-pyrolysis by microwave-assisted in fluidized bed based on bimetal-loaded HZSM-5/MCM-41 core-shell catalyst

Abstract

Enzymatic hydrolysis lignin (EHL), lignosulfonate (LS), alkali lignin (AL), and hydrolysis lignin (HL) residues are mostly burned for heating in industrial production, which greatly wastes resources and pollutes the environment. In this study, we investigated the effects of different temperatures and catalyst-to-biomass mass (C/B) ratios on the relative content of hydrocarbons in the products by microwave-assisted pyrolysis in a fluidized bed. Co and Ni bimetal-loaded molecular sieve with core-shell structure (Co-Ni@H/M) was used as the catalyst. The main component of waste plastic, polyethylene (PE), was pyrolyzed with these four lignin residues to prepare monocyclic aromatic hydrocarbons (MAHs), and the mechanism of synergistic interaction in co-pyrolysis was investigated. It was shown that the maximum liquid phase yield and hydrocarbons relative content were obtained at 550 °C when lignin residues were pyrolyzed alone. Compared with the pyrolysis of lignin residues alone, the liquid phase and gas phase yields of co-pyrolysis were improved, while the solid phase yield decreased. Moreover, the temperature for maximum liquid phase yield and hydrocarbons relative content were reduced to 500 °C. Further exploration of the liquid phase products revealed that the relative contents of hydrocarbons in the four lignin residues and PE (EHL-PE, LS-PE, AL-PE, and HL-PE) co-pyrolysis products at 500 °C were 49.6 %, 33.1 %, 37.7 %, and 43.2 %, respectively, with MAHs as the main components. The results of the effect of different C/B ratios on the distribution of pyrolysis products showed that Co-Ni@H/M promoted the deoxygenation of oxygenated compounds, especially phenolic compounds, and the conversion of aliphatic hydrocarbons into MAHs by cyclization and aromatization.